Three-dimensional semiconductor devices, such as fin-FETs and tri-gate FETs, have significant performance advantages over conventional planar devices, which include, but are not limited to: better gate control over the channel and less intrinsic gate delay.
However, as the 3D semiconductor devices scale down, the device performance becomes more difficult to improve due to mobility degradation. Carrier mobility is considerably dependent on the channel surface orientation. Specifically, when the channel region is formed of single crystal silicon with the channel surfaces oriented along the {100} crystal planes of silicon, electron mobility is enhanced, but hole mobility is degraded. Alternatively, when the channel region is formed of single crystal silicon with the channel surfaces oriented along the {110} crystal planes of silicon, hole mobility is enhanced, but electron mobility is degraded.
As can be deduced from the above, the {110} silicon surfaces are therefore optimal for forming 3D p-channel FET devices (p-FETs) due to the excellent hole mobility along the {110} planes, which leads to higher drive currents in the 3D p-FETs. However, such surfaces are completely inappropriate for forming 3D n-channel FET devices (n-FETs). The {100} silicon surfaces instead are optimal for forming 3D n-FET devices due to the enhanced electron mobility along the {100} planes, which results in higher drive currents in the 3D n-FETs.
In view of the above, there is a need for providing 3D semiconductor device structures that are located over the same substrate but have different surface orientations (i.e., hybrid surface orientations), which provide optimal carrier mobility in respective 3D FET devices.
A need also exists to provide a method to form an integrated semiconductor device that comprises complementary 3D FETs with hybrid channel orientations, i.e., including 3D n-FETs with channels oriented along a first set of equivalent crystal planes that provide relatively higher electron mobility, and 3D p-FETs with channels oriented along a second, different set of equivalent crystal planes that provide relatively higher hole mobility.